[Collins] Product detector for 75A-2 and 75A-3 Receivers

[Al Parker]

Hi Folks,
    I, abt 5 yrs ago, found some info on this subjected Prod. Det. on the
web, at a site: http://military radio.com /(etc.) which no longer exists.
I did make a paper cc of the installation/operating instructions &
schematic, which match Glen's good memory.  If anyone would like, I can
scan them & send via email.
    Also there was an article in Nov. 1960 CQ mag entitled "Modifying The
75A-3 Receiver for Improved SSB Reception."  I have that mag also.  Plus,
when I got my 75A-3 almost 7 yrs ago, from an old friend of mine, it had
the needed plug-in turret socket for building the Prod. Det.   I don't
remember now if the mag came too.  The rcvr had belonged to the
father-in-law of my friend, who I had also known, so there's provenance to
the rcvr for me.  I havne't built the unit yet, but will someday when I
get a round tuit.
    I also have a note, "Feb. '78 HR, 51J- SSB", so maybe that's another
article.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.thecompendium.net/radio/
http://www.hammarlund.info

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----- Original Message ----- 
Date: Fri, 6 May 2005 13:08:15 -0700 (PDT)
From: Glen Zook <gzook at yahoo.com>
Subject: Re: [Collins] Product detector for 75A-2 and 75A-3 Receivers

There were actually a couple of different companies
that made product detectors for the 75A2 / 75A2A /
75A3.  You had to drill a hole under where the Collins
logo was.  However, if you ever had to remove the
adaptor you could put the logo back on and everything
looked "factory".

The reason for the hole was that the adaptor had its
own BFO (tunable) and you had to adjust the frequency
by a shaft that came out the front panel through the
hole.  The escutcheon was held on by screws going
through the two holes that the logo was originally
mounted.

I did not have one.  But, K9LHC had a 75A3 that had
the product detector added that he used for several
years.  As far as I know it did a great job.

You put the receiver in the "FM" position to receive
SSB or CW.

In the past I have made a solid-state product detector
using 2 germanium diodes and associated resistors and
capacitors for 2 different 75A2 receivers.  I brought
the BFO over to the NBFM socket and put the product
detector into a project box and plugged it into the
NBFM socket.  It worked very well as well as the
commercial types.

My present 75A3 has a Collins NBFM adaptor and my 75A2
has one of Howard Mill's product detectors.
Therefore, I haven't had the need to build another
product detector for them.  I do have a Collins 51J2
that I might build a solid-state product detector for
some day.

Glen, K9STH